This code has been running daily for about 20 years. I think I copied from Sergey.

PARAMETERS pc_attachmentname, pc_subject, ;
  pc_mailtext, pc_addresslist
LOCAL trycount

loMail = NEWOBJECT("lf_cdomail","cdomaillib")
WITH loMail
  *-- Create error collection
  .oErrors = CREATEOBJECT("Collection")

  .cServer = oApp.gc_smtpserver
  .nServerPort = oApp.ln_cdoserport
  *-- Use SSL connection
  .lUseSSL = oApp.ll_cdousessl
  .nConnectionTimeout = oApp.ln_cdotimeout && Default 30 sec's
  *-- Do not use cache for cHtmlBodyUrl
  .lURLGetLatestVersion = oApp.ll_cdogetver
  *-- Use SMTP Server Port
  .nSendUsingPort = oApp.ln_cdouseport

  *-- The following lines are required
  * 	if your SMTP server requires basic authentication
  .nAuthenticate = oApp.ln_cdoauthen

  .cUserName = oApp.gc_smtpuser
  .cPassword = oApp.gc_smtppass
  .cFrom =  oApp.gc_smtpfrom

  *-- Use use testaddr for mail testing
  IF  oApp.gl_mailtest
    .cTo = oApp.gc_testaddr
  ELSE
    .cTo = pc_addresslist
  ENDIF
  .cCC = ""
  .cBCC = ""
  .cHtmlBody = ""

  .cAttachment = ""

  *-- Attachments are optional Comment this line out if there are no attachments
  IF NOT EMPTY(pc_attachmentname)
    .cAttachment =  pc_attachmentname
  ENDIF
  .cSubject = pc_subject

  .cHtmlBody = pc_mailtext

  .cTextBody = pc_mailtext

  trycount =1
  DO WHILE trycount < 4
    IF .Send() <> 0 AND trycount = 3
      DO notice WITH "Mail Sending Error"
      EXIT
    ELSE
      EXIT
    ENDIF
    trycount = trycount +1
  ENDDO
ENDWITH
RELEASE loMail
RETURN

>>"Connection Rejected"
>>if I remember correctly Office 365 requires oAuth 2.0 authentication and the port can't be 25 (maybe 465 or 587), TLS 1.2
>>You could try to send mail with normal CDO with the same parameters (port 25, w/o authentication) just to see if it is possible or what error message this will return.
>>
>
>Thanks. For now, I'm trying this without Office 365 involved at all for simplicity. That's the reason for using the free online SMTP server. I tried setting smtpAuthMethod and that doesn't change anything (which makes sense, based on the docs).
>
>I tried your CDO code below and that also fails to send with the error:
>
>OLE IDispatch exception code 0 from CDO.Message.1: The transport failed to connect to the server.
>
>That makes me think that maybe the note in the original error message about a firewall issue may be the key to solving this. (I hate this kind of stuff.)
>
>Tamar
>
>>This works for me (I don't receive any eMail though)
>>

>>SendCDOMail()
>>
>>
>>FUNCTION SendCDOMail()
>>SET STEP ON 
>>    LOCAL loCDOMesage AS CDO.Message
>>    LOCAL loCDOConfig AS CDO.Configuration
>>
>>    lcSchema    = [http://schemas.microsoft.com/cdo/configuration/]
>>    loCDOConfig = CREATEOBJECT([CDO.Configuration])
>>    WITH loCDOConfig.FIELDS
>>         .ITEM(lcSchema + [smtpserverport])   = 25
>>         .ITEM(lcSchema + [sendusing])        = 2
>>         .ITEM(lcSchema + [smtpserver])       = "smtp.freesmtpservers.com"
>>         .ITEM(lcSchema + [smtpauthenticate]) = 0
>>         .ITEM(lcSchema + [sendusername])     = ""
>>         .ITEM(lcSchema + [sendpassword])     = ""
>>         .ITEM(lcSchema + [smtpusessl])       = .f.
>>         .UPDATE()
>>    ENDWITH
>>    loCDOMesage = CREATEOBJECT([CDO.Message])
>>    loCDOMesage.Configuration = m.loCDOConfig
>>    loCDOMesage.BodyPart.Charset     = "utf-8"
>>
>>    WITH loCDOMesage
>>         .From     = "from@somemail.com"
>>         .To       = "to@somemail.com"
>>         .Subject  = "This is a test"
>>         .HTMLBody = "Test of the body contets"
>>         .HTMLBodyPart.Charset = "utf-8"
>>         .TextBodyPart.Charset = "utf-8"
>>         TRY
>>            .Send()
>>         CATCH TO oError
>>            MesageBox(oError.Message)
>>         ENDTRY
>>    ENDWITH
>>
>>    loCDOMesage = NULL
>>    loCDOConfig = NULL
>>    RELEASE loCDOConfig, loCDOMesage
>>RETURN ""
>>

>>
>>***** UPDATE
>>Maybe Chilkat smtpauthenticate equivalent is TRUE by default?
>>Maybe if you change it to FALSE it will work?
>>
>>
>>>I'm just getting started replacing an old email module I wrote for a client that doesn't seem to be working for their customers anymore.
>>>
>>>For various reasons, choosing to do this with Chilkat and the new ChilkatVFP wrapper. I've figured out the code I need to create and send an email, but I'm struggling in testing it. When I tried to configure it to use the SMTP server associated with my Office365-based Exchange Server, I got authentication errors.
>>>
>>>I poked around and found a cool site that provides a test SMTP server online so you can test email issues (https://www.wpoven.com/tools/free-smtp-server-for-testing). Even found a different site that lets you test sending via SMTP (https://smtpserver.com/smtptest). When I use the second site to send an email using the first site's server, the email goes through without error, so I know I've got the right SMTP settings.
>>>
>>>But when I use my code to try to send via the first site, I time out. This is really simple code, just to make sure I can make it all work. After the necessary SET PATH and SET CLASSLIB, it's just:
>>>
>>>

>>>loEmail = CREATEOBJECT('Email')
>>>loEmail.Subject = 'This is a test'
>>>loEmail.Body = [Here's some content.]
>>>loEmail.From = 'tamar@istesting.com'
>>>?loEmail.AddTo('tamar@didthiswork.com')
>>>
>>>loMailMan = CREATEOBJECT('MailMan')
>>>loMailman.smtphost = 'smtp.freesmtpservers.com'
>>>loMailman.smtpport = 25
>>>?loMailman.Sendemail(loEmail)
>>>_cliptext = loMailMan.lasterrortext
>>>

>>>
>>>The error message I get is:
>>>
>>>

>>>ChilkatLog:
>>>  SendEmail:
>>>    DllDate: Oct 27 2023
>>>    ChilkatVersion: 9.5.0.96
>>>    UnlockStatus: 0
>>>    Architecture: Little Endian; 32-bit
>>>    Language: ActiveX
>>>    VerboseLogging: 0
>>>    Auto unlock for 30-day trial
>>>    UnlockStatusMsg: Unlocked for 30-day trial
>>>    UnlockStatus: 1
>>>    sendEmailInner:
>>>      ReadTimeout: 30000
>>>      renderToMime_pt1:
>>>        createEmailForSending:
>>>          Auto-generating Message-ID
>>>        --createEmailForSending
>>>      --renderToMime_pt1
>>>      sendMimeInner:
>>>        ensureSmtpSession:
>>>          ensureSmtpConnection:
>>>            smtpParams:
>>>              SmtpHost: smtp.freesmtpservers.com
>>>              SmtpPort: 25
>>>              SmtpUsername: 
>>>              SmtpSsl: 0
>>>              StartTLS: 0
>>>            --smtpParams
>>>            smtpConnect:
>>>              smtpHostname: smtp.freesmtpservers.com
>>>              smtpPort: 25
>>>              connectionIsReady:
>>>                SMTP host changed.
>>>                Need new SMTP connection...
>>>              --connectionIsReady
>>>              smtpSocketConnect:
>>>                socket2Connect:
>>>                  connect2:
>>>                    connectSocket_v2:
>>>                      connect_domain:
>>>                        Connection attempt failed.
>>>                        maxWaitTimeMs: 30000
>>>                        totalMsWaitedSoFar: 17550
>>>                        Failed.
>>>                      --connect_domain
>>>                    --connectSocket_v2
>>>                    ConnectFailReason: Connection rejected
>>>                    A few possible causes for a connection being rejected are:
>>>                    - A firewall (software or hardware), such as Windows Firewall, is blocking the connection .
>>>                    - Nothing is listening at the remote host:port
>>>                  --connect2
>>>                --socket2Connect
>>>                Failed to connect to SMTP server..
>>>              --smtpSocketConnect
>>>            --smtpConnect
>>>          --ensureSmtpConnection
>>>        --ensureSmtpSession
>>>      --sendMimeInner
>>>    --sendEmailInner
>>>    Failed.
>>>  --SendEmail
>>>--ChilkatLog
>>>

>>>
>>>Any suggestions about what I'm missing here?
>>>
>>>Tamar